Electrothermal fragmentation



P 28, 1965 F. M. BAILEY 3,208,674

ELECTROTHERMAL FRAGMENTATION Filed Oct. 19; 1961 3 Sheets-Sheet 1INVENTOR. EQA/vcu M BAILEY p 8, 1965 F. M. BAILEY 3,208,674

ELECTRO'I'HERMAL FRAGMENTATION Filed Oct. 19, 1961 3 Sheets-Sheet 2INVENTOR. Y Ham/0: M Aim 5y p 23, 1965 F. M. BAILEY 3,208,674

nwcwnownnnmn FRAGMENTATION Filed Oct. 19. 1961 3 Sheets-Sheet sINVENTOR. FRANCIS M 84/45? United States Patent 3,208,674 ELECTROTHERMALFRAGMENTATION Francis M. Balley, Roanoke, Va., asslgnor to. GeneralElectric Company, a corporation of New York Filed Oct. 19, 1961, Ser.No. 146,307 5 Claims. (Cl. 241-1) This invention relates to thefragmentation of rocks and rock formations by means of electricalenergy. More specifically the invention relates to the breaking of rocksby means of a thermal condition set up within the rock .as a result ofan electrical current flowing through a 3,208,674 Patented Sept. 28,1965 'break through ofthe channel occurs, or a low frequency source ofpotential (including direct current) may be requires explosives to beused more than once, necessitating additional safety measures andentailing time consuming operations as well as additional cost. Thepresent invention is concerned with a method and apparatus whereby largefragments of rock produced as a result of primary blasting in a miningoperation may be further reduced in size by electrical energy.

The shattering effect of a stroke of natural lightning is well known,and artificial'lightning bolts have produced similar destructive forceswhich appear to be usable in the fragmentation of solids such as rocks,ore deposits and the like. It has been observed, for example, that whenhigh voltage is supplied through point electrodes placed on the surfaceof a body of rock a current conducting path through the body will occur.It is believed that a thermal break through is produced as a result ofcurrent which flows between the electrodes into the body of rock, thecurrent produced causing the'path through the rock to heat up andthereby set up internal pressures as a result of temperaturedifferentials along cleavage planes or in areas along the path of thecurrent where the water of crystallization is changed to steam as aresult of the heat produced by the electric current. It has been foundthat rock bodies containing-ore that is semiconductive are readilyfractured also by the application of electrical energy somewhat in themanner as has been described. However, the fragmentation of rocks ofother types and formations is also feasible making use of electricalenergy.

It has been found that the frequency and magnitude of the electricalforce applied to a rock body largely determine the extent of breakthrough, and it appears that within limits the higher the temperature ofthe rock body the more readily a current conducting path or channel isformed.

Normally it has been shown that current conducting channels are formedin rock formations by subjecting a body of rock to high voltage at highfrequencies (250 kilocycles to 100 megacycles) through two or moreprobes attached to the surface of the body at spacedapart locations. Thehigh frequency energy tends to raise the temperature of the rock bodythereby causing a breakdown of the dielectric and a consequent reductionin electrical resistance to form conductive channels or superimposed onthe channel, or a high voltage pulse may be discharged through thechannel that is already formed by the high frequency source. Each ofthese three methods has been successful in producing an electrical breakthrough of sufficient electrothermal effect to shatter rock bodiessubstantially.

High frequency apparatus of necessity must be connected to the aforesaidprobes by means of costly, coaxial cables, and a control must beprovided to adjust the apparatus as the. load changes when the currentcarrying path ruptures in order to safeguard the high frequencygenerator. Furthermore, the high frequency output (a range from 250kilocycles to approximately megacycles has been proposed) therebyrequiring not only costly and complicated'generating apparatus, but alsoequally costly and complex means for impedance matching and attachmentto the load. With high frequency generators of the type referred toabove there is also a problem of radio frequency interference in respectto commercial and government radio communications as well as thepossibility that explosive detonators in the vicinity of the miningoperation may he accidentally exploded. The present invention isdirected to apparatus for fragmentation of rocks and rock formationsthat does not require high frequency generators, that requires nocircuits or arrangements for superimposing one frequency upon anotherand that presents few, if any, impedance matching problems. While someof the devices pertaining to the invention are unique in theirapplication to electrothermal fragmentation of rocks and the like, theunique method taught in the invention is capable of being performed byconventional electrical apparatus.

It is therefore an object of this invention to provide a simple andeffective method for physically disrupting rock formations solely bymeans of electrical energy.

Another object of the invention is to provide unique devices for theapplication of electrical energy to the fragmentation of rocks and rockformations.

By experiment it has been shown, as indicated above, that. variousconditions of rock bodies, e.g., temperature, striation, composition, etcetera, directly relate to the effectiveness of utilizing electricalenergy for the fragmentation or physical disruption of rock bodies andthe like. Similarly, as also related above, characteristics of theelectrical energy applied to rock bodies for purposes of fragmentation,such as frequency, voltage, superimposition of frequencies, et cetera,are equally determinative in the effectiveness of utilizing electricalenergy for this purpose. Additionally, however, it has been found thatcertain factors, heretofore, undisclosed, are even more effective in thefragmentation of rock bodies through the utilization of electricalenergy.

It appears that the clue to effective utilization of electrical energyfor fragmenting rock bodies lies within the interstices of the rockformations. The inclusion in these formations of conductive particles,entrapped globules of the water of crystallization, voids between rockparticles or layers and the like has been found to offer a means forimproving upon previous attempts in fragmentation or disruption of suchformations by electrical energy to an extent not heretofore understood.For example, rock formations that have been processed by spraying,immersing. or otherwise treated with water have been found to break intofragments under electrothermal stress from the application of electricalenergy far more effectively than those which have not. The use of steamin a similar manner is equally effective. Furthermore, it has been foundthat when rock formations-are so processed, high frequency electricalenergy is not normally required, and that very effective fragmentationcan be obtained merely by discharging direct current sources, e.g.charged capacitors, through therocit formation. Low frequencyalternating current can also be used with comparable effectiveness.

It is believed that rock formations receiving aqueous treatment, asindicated above, more readily form current conducting channels or. pathsor that the dielectric properties of the rock formation are changed in amanner to more easily produce fractures under the stress of high voltageelectrical energy. In other words the present invention provides a meansfor forming current conducting paths in a rock body without resorting tothe heating effect of the high frequency energy for breaking down thedielectric of the rock formation.

It is, therefore, a further object of this invention to provide a methodfor the fragmentation of rock bodies by electrical energy includingpre-treatment by water or steam.

Since many rock formations contain water-soluble salts and the likewhich reduce the resistance of current carrying channels when treatedwith water or steam, as described above, it follows that for thoseformations not so provided, a conductive aqueous solution, such as saltwater, may be utilized with equaletfectiveness in the manner previouslydescribed.

It is therefore a still further object of this invention toprovide amethod for the fragmentation of rock bodies by electrical energyincluding pro-treatment by a conductive, aqueous solution.

Another object of this invention is to provide a method for fragmentingrock bodies by electrical energy including pre-treatment of the body byan electrolyte.

Still another of the objects of this invention is the provision of amethod for the fragmentation of rock bodies by electrical energyincluding pre-treatment by a conductive liquid.

A further object of this invention is to provide a method for thefragmentation of rock bodies by electrical energy including theformation of a conductive liquid for the pre-treatment of the rockbodies.

The novel features of the invention are set forth with particularity inthe appended claims. The invention itself, however, both as to itsorganization and method of operation, together with further objects andadvantages thereof, may best be understood by referring to the followingdescription and the accompanying drawings.

In these drawings:

FIGURE 1 is a circuit diagram of a high voltage source of electricalenergy suitable for fragmenting rock bodies according to the presentinvention.

FIGURE 2 illustrates the application of electrical energy to a rockbody, the'electrical energy being derived from a source as indicated inFIGURE 1.

FIGURE 3 illustrates the basic principle of the present invention inconnection with pre-treating a rock body with a conductive liquid.

FIGURE 4 illustrates diagrammatically the use of steam in thepre-treatment of a rock body according to the present invention.

FIGURE 5 is a diagrammatic view of the application of the teaching ofthe present invention to a rock face, as in quarrying operations.

FIGURE 6 is a further modification of the device shown in FIGURE 5.

FIGURE 7 illustrates the manner in which contact may be made withirregular rock bodies for the application of electrical energy accordingto the present invention.

FIGURE 8 is an illustration as to the manner in which the teaching ofthe invention may be applied to fragmentation of rock formations instripping operations.

FIGURE 9 illustrates an application of the teaching of the presentinvention to crushing rocks into very small sizes.

Referring now to FIGURE 1 a transformer T-1 is energized through aswitch 8-1 from a source of 115 volt, 60 cycle alternating current viaan autotransformer AT, the output of the transformer T-l being of theorder of 30 kilovolts. In order to obtain still higher voltage thesecondary or output of transformer T-l is fed through the rectifiers R04and RC4 and the current limiting resistors R-2, R-3 and R4 to a pair ofcapacitors C-1 and C-2, which are alternately charged on successivehalves of the cycle in parallel, so that their potentials are additiveas a result of the series connection illustrated in the circuit ofFIGURE 1. Consequently when these capacitors are fully charged, apotential is obtained across them approximately equal to 60 kilovolts,this potential appearing across the resistors R7, R6 and R-5 in seriesand the values of the resistors being chosen so that only a very smallpercentage of this potential appears across the resistor R7. The highpotential across resistors R-5 and R6 is also applied across the gapsformed by G-1 and G-3 and by 6-2 and G4; however, these gaps normallyare set so that no fiashover occurs at the applied potential.

The 115 volt, 60 cycle alternating current source is also connectedthrough switch 8-1 and a rectifier RC-3 to charge a capacitor C4 via alimiting resistor Rl under control of a switch S-2 so that when theswitch 8-2 is thrown to contact X the capacitor is charged and when theswitch. 8-2 is thrown to contact Y the capacitor is discharged throughthe primary of a step-up transformer T-2. When capacitor C4 isdischarged in this manner the secondary of the transformer T-2 suppliesa high voltage pulse through the; capacitor C3 of sufiicient magnitudeto break down the gap formed by 6-2 and 6-3, and as a result the highpotential of the capacitors C-1 and C4 in series overcomes the gapformed by G1 and 6-3 so that the total potential of the capacitors isapplied across the resistor R-7 and to the probes P-1 and P-2. In themanner described high voltage direct current pulses are supplied to theprobes P-1 and P-2.

Using the electrical pulse generator described above, a rock body RK asshown in FIGURE 2 may be fragmented by applying the probes P-1 and P-2,respectively, to contact positions CT-l an d CT-2 on the surface of therock body. Ordinarily a single high voltage pulse may not be sufficientto fragment the rock body; however, repeated pulses may be delivereduntil an electrical current carrying channel is developed along thedot-dash" line indicated in FIGURE 2 between the contact positions CT-land GT4. This current carrying channel normally occurs through the rockbody although there may be occasional flash-overs" on the rock surface.

As previously discussed, the formation of acurrent carrying channelthrough the rock body is necessary in order to generate sufiicient heatwithin the rock body to bring about disruption of the rocks structure.In ore bearing rock formations conductive paths may already be formed orpartially formed due to the semi-conductive properties of the oredeposits; however, in most rock formations it has been found that therate of forming a current carrying channel is greatly enhanced, if notalto- The conductive liquids may be the rock body as in FIGURE 3 whereina nozzle N provides a spray of water or electrolyte from a source WSwith which the rock RK is pre-treated prior to a high voltage pulsebeing injected into the rock body via the probes P-1 and P4. The rockbody may be immersed in the conductive fluid, or it may be subjected toa spray of steam, as indicated in FIGURE 4, from a tank BB via a nozzleNN. It is to be noted that while steam per se is not a conductive agent,as with pure water, many rock bodies contain salts or other watersoluble substances, which in combination with water or steam produceconductive liquids or the equivalents. Since it is desired to have acurrent carrying channel form within the rock body in order to set upthe stresses that bring about fragmentation rather than make the surfaceof the rock body more conductive, it is necessary to insure that thesurface of each rock body treated with conductive fluid becomes drybefore the high voltage impulse is applied via the probes P-1 and P-2.With most aqueous fluids normal evaporation is suflicient for thispurpose; however, forced drying of the rock body by moving air orotherwise may be employed.

FIGURE 5 illustrates the manner in which the teaching of the inventionmay be utilized'to scale off fragments from a rock face. Holes HL ofrelatively small diameter are drilled into a rock face RF above the areathat is to be fragmented and a conductive liquid is injected into them.The probes P-1 and F4 from the high voltage impulse device described inFIGURE 1 are then inserted into similar holes 1-1-1 and H-2,respectively, so that when the high voltage pulse is applied aconductive path is formed internally of the rock formation between thetips of the probes. The area SA (see dotted lines in FIGURE 5)substantially will have absorbed the injected conductive liquid so thatthe electrical break down and consequent disruption of the rock facewill occur in that area.

FIGURE 6 illustrates a furthermodification of the arrangement shown inFIGURE 5. According to FIG- URE 6 the rock face RFF is sprayed by aconductive liquid, some of which is absorbed by the rock face. Since thesurface of the rock face will evaporate the liquid more rapidly than theinterior, some of the liquid will remain to assist in forming currentconductive paths internally, as previously explained. A pan PN supportedby a movable rarnp BR, which may be carried on the boom of a crane orshove], is provided with a pair of probes P-1 and P4 separated by aninsulating arm IS mounted on the pan. The probes P-1 and P-2 in thisinstance are arranged to have points or pointed tips so that the pan PNcan be forced against the rock face RFF thereby forcing the tips intothe face at points CT-l and'CT-Z, for example, thereafter a high voltagepulse is provided to the probes. In this manner a rock face may bechipped away more rapidly in small areas such as SA (see dotted lines ofFIGURE 6).

FIGURE 7 shows the manner in which individual rocks may be fragmentedusing the teaching of the invention. After pretreatment with aconductive liquid and drying a rock RK has applied to it the tongs TG-land TG-2 so that current carrying paths may be formed internally of therock RK between the tips of the tangs T-l, T-Z and T-3 and the tang T-4(as indicated by the dash-dot lines of FIGURE 7), the tongs TG-l havingan insulating tang IT for mechanical support. The high voltage impulsein this instance is supplied to the cables CB-l and CB-2 in the samemanner that has previously been explained for the probes P-1 and P-2,respectively. The tangs of each of the tongs may be spring urged toclose upon the rock so that operating personnel may stand clear when thehigh voltage impulse is delivered.

A unique adaptation of the invention is illustrated in FIGURE 8; namely,a vehicle capable of performing strip mining operations. A wheeled ortracked vehicle V ing cables CB4 and CB-2 connected to a high voltageimpulse source (not shown). A means is also provided in the nature of aspray WS for distributing a conductive liquid in the path of thevehicle. The vehicle moves .slowly over the area to be stripped, and maybe selfpropelled or pushed by a tractor or the like. The rate of travelof the vehicle V is such that the conductive liquid will seep into thepores of the rock formation via gravity thereby tending to set upcurrent carrying channels in the sub surface of the rock as the probesP-1 and P-2 progre'ss, recurring high voltage impulses being supplied tothem, so that fragments will be broken loose substantially from an areaas indicated by dotted lines and picked up by a continuously movingconveyor CVB and de posited in a hopper HP.

A form of electrical rock-crusher is illustrated in FIG- URE 9. Here aconveyor belt CVR moves continuously to deliver rocks RK from a hopperHP-l to a nozzle N which sprays conductive liquid from a pipe WSC uponthe rocks. Thereafter the rock progresses to be contacted by flexiblefingers F-l and F-2, respectively, attached to the probes P-1 and P-Z,which are connected by cables to a high voltage impulse source such asthat described in connection with FIGURE 1, above. Forced air drying(not shown) may be employed to dry the surface of the rocks beforecontacting the fingers F-l and F-2; however, normal evaporationordinarily will provide a dry rock surface so that surface flash-oversoccur only infrequently as the high voltage impulses are applied by thefingers F-l and F-2. Consequently the current carrying paths formed inthe rocks as a result of being treated with the conductive liquid formthe major paths of current discharge,'and the rocks RK are fragmented,as previously described, the fragments being carried by the conveyor CVBinto another hopper HP-Z and delivered into a bin BN.

While this invention has been explained and described with the aid of aparticular embodiment thereof, it will be understood that the inventionis not limited thereby and that many modifications will occur to thoseskilled in the art. It is therefore contemplated by the appended claimsto cover all such modifications as fall within the scope and spirit ofthe invention.

What is claimed is:

l. A method for fragmenting a rock by electrical energy comprising thesteps of introducing steam into the interstices of the rock, attachingelectrodes to the surface of the rock, and applying electrical potentialacross the electrodes.

2. A method for fragmenting a rock by electrical energy comprising thesteps of introducing a conductive fluid into, the interstices of therock, attaching electrodes to the surface of the rock, and applying ahigh voltage direct current impulse across the electrodes.

3. A method for fragmenting a rock by electrical energy comprising thesteps of introducing a conductive fluid into the interstices of therock, attaching electrodes to the surface of the rock, and applying highvoltage direct current across .the electrodes.

4. A method for fragmenting a rock by electrical energy comprising thesteps of spraying the rock with a conductive fluid, allowing the fluidto seep into the interstices of the rock, drying the surface of therock, attaching electrodes to the surface of the rock, and applyingelectrical potential across the electrodes.

5. A method for fragmenting a rock by electrical energy comprising thesteps of immersing the rock in a conductive fluid, allowing'the fluid toseep into the interstices of the rock, removing the rock from theconductive fluid, drying the surface of the rock, attaching electrodesto the surface of the rock, and applying electrical potential across theelectrodes.

(References on following page) 7 8 References Cited by ihe Eer 3,103,9759/63 Hanson 166-421 Parker h d 2 2 1 OTHER REFERENCES Booth 266-1 5Dustless Breaking of Rocks Electrically, Translated Yellott 241-1 fromGornyy Zhumal, copy in Scientific Library TN s p 166 11 1.M783 (MiningJournal), September 1960. La Tour Mining Congress Journal, May 1961, pp.53-55. Bourquet 241- 1 WILLIAM W. DYER, J R., Primary Examiner. Hm 2413010 MEYER PERLIN, I. SPENCER OVERHOLSER, Becker 24130 ANDREW R. JUHASZ,Examiners.

1. A METHOD FOR FRAGMENTING A ROCK BY ELECTRICAL ENERGY COMPRISING THESTEPS OF INTRODUCING STEAM INTO THE INTERSTICES OF THE ROCK, ATTACHINGELECTRODES TO THE SURFACE OF THE ROCK, AND APPLYING ELECTRICAL POTENTIALACROSS THE ELECTRODES.